In a gas turbine engine, air is pressurized in a compressor and then mixed with fuel and ignited in a combustor for generating hot combustion gases. The gases flow through turbine stages that extract energy therefrom for powering the compressor and producing useful work. A turbine stage includes a row of turbine buckets extending outwardly from a supporting rotor disc. Each turbine bucket includes an airfoil over which the combustion gases flow. The airfoils are generally hollow and may be provided with air bled from the compressor for use as a coolant during operation.
Each turbine bucket includes a blade body and a tip cap. Due to the environment in which the tip cap operates, the tip cap should be oxidant resistant. The tip cap also is prone to bulging due to creep. Most alloys with sufficient creep strength do not have sufficient resistance to oxidation. Most alloys with adequate oxidation resistance do not have sufficient creep strength. Those alloys that do have adequate properties for both creep and oxidation generally are not available except as custom cast billets. Such custom billets then have to be worked at great expense to form a finished product. Other alternatives include the use of an aluminized coating to the underside of the tip cap.
Thus, there is a desire for a suitable material that provides both adequate oxidation resistance and sufficient creep strength. Preferably, the material should be reasonable in terms of costs and workability.